Entity tax identification number Entity Tax Identification Number Employee-rollover EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Maximum Maximum [Member] Legal Entity [Axis] Legal Entity [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] EBP, Description of Plan [Table] EBP, Description of Plan [Table] Mutual funds Mutual Fund [Member] Total Fully Corrected Under Voluntary Fiduciary Correction Program (VFCP) and Prohibited Transaction EBP, Schedule of Delinquent Participant Contribution, Corrected EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Annual compensation to total compensation, percent EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage Participant contribution, automatic, annual increase in deferral rate, percent EBP, Participant Contribution, Automatic, Annual Increase Deferral Rate Annual increase in percentage of eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) until the contribution reaches maximum threshold. Total Deductions EBP, Change in Net Asset Available for Benefit, Decrease Total investments EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Money market fund Money Market Funds [Member] Level 1 Fair Value, Inputs, Level 1 [Member] EBP, Investment, Fair Value and NAV [Abstract] EBP 002 EBP 002 [Member] EBP 002 Total Assets EBP, Asset Assets EBP, Asset [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Additions EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Payment of Benefits EBP, Payment to Participant [Policy Text Block] Account balances subject to lump sum distribution (less than) EBP, Payment of Benefits, Terminated Participants, Account Balance Threshold Amount For Mandatary Lump Sum Distribution EBP, Payment of Benefits, Terminated Participants, Account Balance Threshold Amount For Mandatary Lump Sum Distribution Amendment Flag Amendment Flag Basis of Accounting EBP, Basis of Accounting [Policy Text Block] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Table] EBP, Investment, Number of Shares Number of Units or Shares Held EBP, Investment, Number of Shares EBP, Description of Plan and Accounting Change [Abstract] EBP, Investment, Fair Value and NAV EBP, Investment, Fair Value and NAV [Table Text Block] EBP, Participant-Directed EBP, Participant-Directed [Member] Employer contribution vesting service period (in years) EBP, Employer Contribution Vesting Service Period Minimum Vesting service period for company contribution and/ or investment earning to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions. EBP, Schedule of Delinquent Participant Contribution [Abstract] Investments [Domain] Investments [Domain] Use of Estimates EBP, Use of Estimate [Policy Text Block] EBP, Schedule of Asset Held for Investment EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract] Risks and Uncertainties EBP, Risk and Uncertainty [Text Block] Employer EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash EBP, Schedule of Delinquent Participant Contribution [Line Items] EBP, Schedule of Delinquent Participant Contribution [Line Items] Minimum Minimum [Member] Investment Type [Axis] Investment Type [Axis] Total contributions Total contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Employee-payroll EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Dividends EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Employer discretionary contribution amount EBP, Employer Discretionary Contribution Amount EBP, Employer Discretionary Contribution Amount Plan number EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] Description of the Plan EBP, Description of Plan [Text Block] Contributions Pending Correction in VFCP EBP, Schedule of Delinquent Participant Contribution, Pending Correction in VFCP EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Fixed Rate Contribution EBP, Fixed Rate Contribution [Member] EBP, Fixed Rate Contribution EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] S&T Bancorp, Inc. common stock EBP, Employer, Common Stock [Member] EBP, Schedule of Asset Held for Investment [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Table] Total Additions Total Additions EBP, Change in Net Asset Available for Benefit, Increase Investment income: EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Investment, Identifier [Axis] Investment, Identifier [Axis] Participant administrative fees EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense EBP, Employer Contribution, Type [Axis] EBP, Employer Contribution, Type [Axis] EBP, Employer Contribution, Type Administrative Fees EBP, Administrative Fees Policy [Policy Text Block] EBP, Administrative Fees Policy Withdrawals, transfers, fees and forfeitures EBP, Change in Net Asset Available for Benefit, Transfer to (from) Plan, Transfers, Fees And Forfeitures EBP, Change in Net Asset Available for Benefit, Transfer to (from) Plan, Transfers, Fees And Forfeitures Document Information [Line Items] Document Information [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Line Items] 1% of eligible compensation Employer Matching Contributions, First One Percent Of Eligible Compensation [Member] Employer Matching Contributions, First One Percent Of Eligible Compensation EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Table] Contribution to total compensation, percentage EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Level 2 Fair Value, Inputs, Level 2 [Member] Contributions Corrected Outside VFCP EBP, Schedule of Delinquent Participant Contribution, Corrected Outside VFCP EBP, Tax Status [Table] EBP, Tax Status [Table] Net increase EBP, Change in Net Asset Available for Benefit, Increase (Decrease) Transactions with Parties-in-Interest EBP, Related Party and Party-in-Interest Transactions [Text Block] EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] Automatic, deferral rate EBP, Participant Contribution, Automatic, Deferral Rate Investments, at fair value: EBP, Investment, Fair Value [Abstract] Distributions to participants EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Dividends EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment Total assets held at end of year EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Accounting Policy [Line Items] EBP, Accounting Policy [Line Items] EBP, Tax Status [Abstract] Maximum vesting percent EBP, Employer Contribution Vesting Percentage Company contribution and/ or investment earning percentage vesting to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions, upon completion of minimum service period or attainment of maximum vesting age Investment Valuation and Income Recognition EBP, Investment [Policy Text Block] Total Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Document Type Document Type Plan Termination EBP, Plan Termination [Text Block] Entity Central Index Key Entity Central Index Key Participant compensation matched, percentage EBP, Participant Contribution, After Tax, Annual Contribution to Eligible Compensation, Percentage EBP, Participant Contribution, After Tax, Annual Contribution to Eligible Compensation, Percentage Next 5% of eligible compensation Employer Matching Contributions, Two To Six Percent Of Eligible Compensation [Member] Employer Matching Contributions, Two To Six Percent Of Eligible Compensation EBP, Risk and Uncertainty [Abstract] EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] Deductions EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Employer forfeited nonvested amount EBP, Forfeited Nonvested Account, Decrease from Employer Contribution EBP, Employer Contribution, Type [Domain] EBP, Employer Contribution, Type [Domain] EBP, Employer Contribution, Type [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Summary of Significant Accounting Policies EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name Schedule H, Line 4a - Schedule of Delinquent Participant Contributions EBP, Schedule of Delinquent Participant Contribution [Text Block] EBP, Schedule of Delinquent Participant Contribution [Table] EBP, Schedule of Delinquent Participant Contribution [Table] Income Tax Status EBP, Tax Status [Text Block] EBP, Participant-Directed and Nonparticipant-Directed Status [Domain] EBP, Participant-Directed and Nonparticipant-Directed Status [Domain] EBP, Participant-Directed and Nonparticipant-Directed Status [Axis] EBP, Participant-Directed and Nonparticipant-Directed Status [Axis] Document Information [Table] Document Information [Table] Total investment income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Level 3 Fair Value, Inputs, Level 3 [Member] Contributions Not Corrected EBP, Schedule of Delinquent Participant Contribution, Not Corrected Net assets available for benefits Net assets available for benefits at beginning of year Net assets available for benefits at end of year EBP, Net Asset Available for Benefit Entity [Domain] Entity [Domain] Contributions: EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Account balances subject to mandatary rollover EBP, Payment of Benefits, Terminated Participants, Account Balance Threshold Amount For Mandatary Rollover EBP, Payment of Benefits, Terminated Participants, Account Balance Threshold Amount For Mandatary Rollover Participant forfeited nonvested amount EBP, Forfeited Nonvested Account Matching percentage EBP, Employer Contribution, Matching Percentage EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]